Use of thermally modified wood in Use of thermally modified wood in building constructions building constructions
Prof.dr. Franc PohlevenProf.dr. Franc [email protected]
University of LjubljanaUniversity of LjubljanaBiotechnical Faculty,Biotechnical Faculty,
Department of Wood Science and Technology,Department of Wood Science and Technology,RoRožžna dolina, Cesta VIII/34na dolina, Cesta VIII/34SI1000 Ljubljana, SloveniaSI1000 Ljubljana, Slovenia
INTRODUCTIONINTRODUCTION
• Different wood modification process:• Thermal• Chemical• Enzimatic
INTRODUCTIONINTRODUCTION
• DIFFERENT HEATING MEDIA:nitrogen, steam, oilVACUUM – A SLOVENIAN METHOD
• Exposure to high temperatures cause severe degradation of cellulose and losses in mechanical properties
INTRODUCTIONINTRODUCTION
• Temperatures from 160 °C to 260 °C• Absence of oxygen• Process of wood modification• Chemical changes in wood cell walls• Changes of wood (=modified wood)
Phases of process (24 h)
drying at 103 °C
vacuuming up to 0,05 bar
heating to 150 °C
heating to T of modif. (3 h)
cooling down
MATERIALS AND METHODS - modificationMATERIALS AND METHODS - modification
SOFTWOOD or HARDWOOD
PROPERTIES OF THERMALLY MODIFIED PROPERTIES OF THERMALLY MODIFIED WOODWOOD
• Improvement of durability and dimensional stability
• Removing of resins• Improvement of resonant (acoustic) properties• Mass loss• Change of physical properties:
• Colour• Reduction of strength and stiffness• Bending strength 10 % – 50 %
Results - change of colourResults - change of colour
S B H
Elm wood
• MASS LOSSES
Spruce: 3 % (190 °C) – 24 % (230 °C)Larch: 5 % (190 °C) – 31 % (230 °C)
MATERIALS AND METHODS – decay testsMATERIALS AND METHODS – decay tests
• DECAY TESTS
mini-block test (Bravery)
cross-section: 10 mm × 5 mm
length: 30 mm
Gloeophyllum trabeum
Coniophora puteana
exposure: 8 weeks
Mass loss (%)
Gt Cp
Spruce untreated 35,2±5,4 56±12
treated 1,5±1,1 8,9±4,4
Larch untreated 34,2±7,7 29,0±2,9
treated 1,17±0,18 0,90±0,21
• DECAY – samples treated at 200 °C
RESULTS – decay testsRESULTS – decay tests
MATERIALS AND METHODS – dimensional stabilityMATERIALS AND METHODS – dimensional stability
• DIMENSIONAL STABILITY
ASE – soaking/ovendrying test (3 cycles)
shrinkage (α) in r, t dim.
20 mm × 20 mm × 20 mm
50 mm × 20 mm × 20 50 mm × 20 mm × 20 mmmm
unorientedunoriented
ABSORPTION OF WATER VAPOUR AT 83 ABSORPTION OF WATER VAPOUR AT 83 % AIR HUMIDITY% AIR HUMIDITY AND T = 25 °CAND T = 25 °C
Exposure atExposure at 83 % 83 % RH and RH and 25 °C 25 °C
RESULTS: absorption of RESULTS: absorption of water vapour – spruce water vapour – spruce
woodwood
RESULTS: absorption of RESULTS: absorption of water vapour – beech woodwater vapour – beech wood
RESULTS: absorption of RESULTS: absorption of water vapour – oak woodwater vapour – oak wood
DIMENSIONAL STABILITYDIMENSIONAL STABILITY (spruce) (spruce)
DIMENSIONAL STABILITY (beech)DIMENSIONAL STABILITY (beech)
DIMENSIONAL STABILITY (oak)DIMENSIONAL STABILITY (oak)
APPROXIMATIONAPPROXIMATION OF REDUCTION OF DIMENSIONOF REDUCTION OF DIMENSIONSS OF OF MODIFIED WOODMODIFIED WOOD SPECIMENS (spruce) SPECIMENS (spruce)
APPROXIMATIONAPPROXIMATION OF REDUCTION OF DIMENSIONOF REDUCTION OF DIMENSIONSS OF OF MODIFIED WOODMODIFIED WOOD SPECIMENS (beech) SPECIMENS (beech)
APPROXIMATIONAPPROXIMATION OF REDUCTION OF OF REDUCTION OF DIMENSIONDIMENSIONSS OF MODIFIED WOOD OF MODIFIED WOOD SPECIMENS SPECIMENS
(oak)(oak)
MATERIALS AND METHODS – MOE AND MATERIALS AND METHODS – MOE AND MORMOR
• MOE, MOR
static three-point bending test
300 mm × 20 mm x 20 mm, absolute dry
Zwick Z-100Zwick Z-100
10 mm/min
MATERIALS AND METHODS - MATERIALS AND METHODS - MOEMOE
• MOE non-destructively
natural vibration analysis in clamped-free conditions
300 × mm 20 mm × 10 mm, absolute dry
12
3
4
56
MATERIALS AND METHODS - MATERIALS AND METHODS - MOEMOE
• MOE non-destructively
inductive proximity sensor
0
2
4
6
8
10
0 0,2 0,4 0,6 0,8 1 1,2
čas (s)
nape
tost
(V
) FFT
νn
dynamic signal analyzerdynamic signal analyzer
• MOR AND MOE of absolute dry samples
0
2000
4000
6000
8000
10000
12000
14000
16000
100 x MOR(spruce-bending)
MOE (spruce-bending)
MOE (spruce-
vibration)
MOE (larch-
vibration)
MP
a
Untreated
Treated, 190 °C
Treated, 210 °C
Treated, 230 °C
RESULTS – MOE and RESULTS – MOE and MORMOR
Laboratory chamber for thermal wood modification
Industrial chamber for thermal wood modification
Silvaprodukt d.o.o., Ljubljana, Sovenia
The first product made from thermally modified wood, modified according to “our procedure”
CONCLUSIONSCONCLUSIONS
• The best characteristics of the products made of modified wood were achieved with wood, modified at temperatures between 180 °C and 210 °C
• In spite of the treatment, the mechanical properties of modified wood are still appropriate for wood to be used in constructions
• Wood modification process can ensure appropriate resistance for diverse ways of utilisation of wooden products, especially in in wet conditions
